Preparation of silica-alumina



Dec. 4, 1951 R N Re. 23,438

PREPARATION OF SILICA-ALUMINA CRACKING CATALYST Original Filed July 24.1950 REGION OFGEL FORMATI N WITHIN 24 MOLES/UTER I K m FINAL S 02CONCENTRATION N 6 M ON MIXING Flfi. 1

8 X g y 2 30 KlNE MATIO V5605 N TIME IN MINUTES F1611 lnvenfor= Umjd B.R \ond Reissued Dec. 4, 1951 PREPARATION OF SILICA-ALUMINA CRACKINGCATALYST Lloyd B. Ryland, El

Shell Development Original No. 2,565,886,

rial No. 175,528, July 24, 1950.

Cerrito, Cali1'., assignor to Company, San Francisco, Calif., acorporation of Delaware dated August 28, 1951, Se-

Application for reissue October 10, 1951, Serial No. 250,622

Matter enclosed in heavy brackets I: appears in the orig'lnal patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

7 Claims.

This invention relates to a. process for the production ofsilica-alumina cracking catalyst.

The object of the invention is to provide a method for the production ofsuperior synthetic silica-alumina cracking catalyst which is applicablefor the production of such catalysts on a commercial scale.

The process in the petroleum industry known as catalytic cracking is inwide use on a large scale. While certain so-called natural catalysts(special acid treated clays) are used in some plants, the most commonlyused catalyst is the so-called synthetic silica-alumina catalyst. Whenit is consideredthat a single catalytic cracking plant has an inventoryof catalyst of several hundred tons, and uses several tons a day offresh catalyst for make-up, it is evident that any practical catalystmust be capable of production in a simple manner on a large scale. Atpresent the commercial synthetic silica-alumina cracking catalyst isgenerally made by forming a dilute slurry of hydrous silica gel byadding sulfuric acid to a solution of sodium silicate, impregnating thehydrous silica gel with aluminum sulfate, and then hydrolyzing thealuminum sulfate by the addition of ammonium hydroxide. While thecatalyst and method of manufacture of the catalyst appear to be quitesimple in general outline, the true nature of the catalytic action andthe mechanism of the deactivation of the catalyst are very complex andlittle understood, and in order to produce an active and stable catalystcertain details in the method of the manufacture must be controlled.Thus the pH, time of washing, etc., are important. See U. S. Patent No.2,478,519. The resultant catalyst which may be prepared in the form ofpowder, microspheroids, pellets, or larger granular fragments, is quiteactive and quite stable against the detrimental influences of hightemperature and steam.

A lengthy and detailed study of the fundamental aspects of this type ofcatalyst has been made. This work brought to light many important factsregarding the physical structure, types of combinations of the silicaand alumina, mode of catalyzing the cracking of hydrocarbons, etc. Forinstance, it is now known that the aluminum may exist in the catalyst inany one of three forms depending upon the details in the procedure ofpreparation. These forms, are namely, free alumina, cationic aluminum,anionic aluminum, and combinations thereof. It is now [know] known thatthe cracking activity is associated with one type of silica-aluminacomplex. As a practical result of this study, a synthetic silica-aluminacracking catalyst was developed which is believed to be superior tosynthetic silica-alumina cracking catalysts previously known. Thiscatalyst which is described and claimed in U. S. Patent No. 2,469,314 ischaracterized physically: (1) by an alumina content which is above thatfound in the usual commercial catalysts and, namely, of the order of18-38%; (2) by having pores which are much larger than those previouslythought optimum and, namely, in the order of -75 Angstroms; (3) by avery low particle density, below 0.95 grams/cc; and (4) by havingassociated with the above characteristics a large available surface. Aspointed out in said U. S. Patent No. 2,469,314, certain details in thepreparation are necessary to obtain an active and stable catalyst havingthese characteristics. As shown in the examples, the catalyst wasprepared under exceedingly acid conditions (pl-1:0), through a properlyaged silica gel, and through the use of aluminum chloride. While thiscatalyst can be produced as therein described, this can only be done ata considerable cost. This is due primarily to the facts (1) that theexceedingly acid conditions require special and costly equipment andresult in a waste of large amounts of acid, (2) that enormous amounts ofpurified water and equipment are required to free the catalyst of alkalimetal salts, (3) that under the exceedingly acid conditions used thetime of set of the hydrogel is very long, therefore requiring very largevessels to afford the necessary residence time, and (4) that aluminumchloride is much more costly than aluminum sulfate. Consequently, it waslater attempted to modify that method of preparation to lower the costto a more economical level, but these attempts failed to produce acatalyst having material superiority over the synthetic silica-alumina.catalyst presently in commercial use.

A method has now been developed whereby a catalyst similar to that of U.S. Patent No. 2,469,314. and even somewhat more active can be producedmore economically. As will be seen from U. S. Patent No. 2,469,314 thebase gel of the described superior catalyst was prepared under highlyacid conditions (pH=O).

According to the method of this invention the base material is nowproduced under less acid conditions; the pH is between 2.8 and 4.1 andpreferably about 3.5. The trick here is to use very concentratedsolutions. Thus, whereas it is the usual practice to produce silicahydrogels having a concentration of $02 between about 3 and 6%,

" Quartz Company) are well 3 it is necessary to employ silica sols ofsuch concentrations that the concentration of S102 is at least 8.5% andpreferably at least about 9.3%. The use of silica sols having suchconcentrations of silica would ordinarily not be practical In the methodof the invention the sol is diluted in a particular manner with waterduring the polymerization. This dilution and the manner in which it iscarried out have an important influence on the character and propertiesof the catalyst. With the base material produced in this manner it ispossible to incorporate the desired large amount of alumina and have itall combine with the silica in the desired particular manner to producea catalyst having the desired properties and the high desired activity.Also, the catalyst produced in this manner can be washed free of solublesalts in conventional plant equipment with reasonable amounts of washwater. It is also possible, using this procedure, to employ aluminumsulfate ininstead of aluminum chloride.

Having set forth the background and the general statements of thepresent method, the method for preparing the catalyst will be describedin more detail.

FORMATION OF THE SILICA SOL A concentrated silica sol is first producedunder acid conditions. The concentration of silica in the sol is atleast 85 grams per liter and preferably 90 to 125 grams per liter. Thissol may be produced by either adding the sodium silicate solution to theacid with mixing, or by simultaneously pumping the sodium silicatesolution and the acid into an acid medium with mixing. In the firstmethod the sodium silicate solution is added until the pH of the sol isbetween 2.8 and 4.1 and preferably about 3.5. In the second case, therates of flow of sodium silicate and acid are adjusted to give a pH ofthe mixture of 2 to 3 and preferably about 2.8, and then the sol isadjusted to a pH between 2.8 and 4.1 by the addition of a small trimmingamount of alkali, e. g. sodium silicate.

As an example of the first case, E Brand sodium silicate (PhiladelphiaQuartz Company) is diluted to 1.28 N (as to Na+) and 3.2 volumes of thesolution are added with stirring to 1 volume 4.1 N sulfuric acid. volumeof acid as basis.) This gives a $01 of pH 3.5 containing 93 grams $102per liter.

As an example of the second case, E Brand sodium silicate is diluted to2.06 N and 1.95 volumes of the solution are added simultaneously with 1volume of 4.07 N H2804 to 1.2 volumes of in plant practice.

water, after which the pH is adjusted from 2.5

up to 3.5 by the addition of a small amount of the sodium silicatesolution.

The preferred acid is sulfuric acid. However, nitric acid orhydrochloric acid can'be used. In the reaction of the sodium. silicatewith the acid to produce the sol a large amount of alkali metal salt, e.g. sodium sulfate, is formed. This salt exerts a considerabledehydrating action, particularly in the concentrated sol, and plays arole in determining the properties of the catalyst. For this as Well asother reasons a sodium silicate having a loweralkali-silica ratio thanthe orthosilicate or metasilicate is preferred. Thus, sodium silicatesolutions having an alkali-silica ratio between about 1:2.5 and 113.9are preferred. The sodium silicates known as E Brand, N Brand and SBrand (Philadelphia suited. The E and (All volumes refer to the iai 4alkali-silica ratio of about Brand has an alkali-silica N Brands have an1:322 and the S ratio of about 1:3.90.

When mixing the acid and the sodium silicate there is a tendency toprecipitate silicic acid, and this tendency is particularly pronouncedwhen preparing a sol of the high concentration specified. The formationof a small amount of precipitate is not particularly harmful. Theformation of a precipitate is minimized (1) by adequate mixing, (2) byusing an acid solution which is stronger than the sodium silicatesolution, and ('3) by maintaining the pH at the stated low value duringthe mixing. While it is preferred to regulate the conditions so as toform the clear sol, the invention does not preclude the presence of suchgelatinous precipitate.

AGING OF THE SOL The silica sol produced as specified will upon standinggradually thicken and finally set to a hard gel. The time of set isdetermined as follows. A 75 cc. portion of the fresh sol is poured intoa 100 cc. beaker. A 3 mm. glass rod 8 cm. long and pointed at one end isplaced in the sol with the point resting on the bottom of the beaker.The rod is allowed to fall from an initial angle of 15 from the verticalto an angle of 30. The point when the rod is held between these anglesis the setting point and the time interval between this point and theformation of the S01 is the time of set (1"). The time of set for anumber of sols and conditions is given by Hurd (Journ. Phys. Chem. [37]37 321 (1938)). The time of set is dependent upon the various factors,including the concentration of silica, the concentration of alkali metalsalt, and the pH of the sol. The region of conditions of concentrationof S102 and pH Where setting occurs within 24 hours with sols made fromsodium silicate having an alkali-silica ratio of 1:3.9 is shown in thegraph Fig. I of the attached drawing. The rectangle A near the top ofFig. I delineates the conditions under which the sol is formed accordingto the method of this inven-- tion.

If the sol is allowed to stand it does not set at once to a gel but thesetting is preceded by a gradual increase in the viscosity. The rate ofthis increase in viscosity is dependent upon the conditions and is afunction of the time of set. Typical rates of increase of the viscosityfor sols having different times of set are shown in the graph, Fig. 11of the attached drawing. It is found, however, that if the reduced timeof set (T/T') (i. e. the actual time divided by the time of set) is usedin plotting the viscosity curves, the curves substantially coincide. Theincrease in the viscosity of the sol is due to the growth of thecolloidal silica miscellae and is a function of the extent of aging ofthe sol. The aging of the sol is of importance in determining theactivity and stability of the catalyst.

In the method of the invention the sol is preferably one which ifallowed to stand would set toa gel in about 10 minutes to 90 minutes andmore preferably in about 15 minutes to 40' minutes. The sol could beallowed to gel and the gel could then be further aged by standing. This,however, does notlyield a catalyst having the desired properties. In themethod of the invention "the sol is not allowed to set and the aging iscarried out in a difierent manner. At a time short of T the increase inthe viscosity is halted, the aging rate is reduced, and setting is.prevented by diluting the sol with water. In other words, at a certainpoint short of setting the polycondensation to a rigid gel is arrestedby dilution while allowing the silica micellae to further age under acidconditions.

DILUTION OF THE SOL monium hydroxide solution. Sodium hydroxide Thedilution of the sol is preferably begun late in the aging period, e. g.where the of set (T/T) is between 0.5 and 0.95 and preferably as near to0.95 T/ T as practically feasible. The preferred method is to begin thedilution as soon as the viscosity corresponds to that of the chosenvalue of T/T' and to continue the dilution at a rate to maintain theviscosity substantially constant. The amount of water required will varysomewhat depending upon the concentration of silica in the sol and thepH; in a typical case it is 2.25 volumes.

The addition of the water may be controlled in response to a continuousviscosity measurement of the sol, using one of the known techniques, andthis addition may beautomatically controlled. One suitable method forcontrolling the addition of the water is through the use of aconsistency controller, e. g. such as used on paper stock, whichmeasures the torque required to rotate a paddle or other mixer at aconstant speed. This measurement may be accomplished by means of acontrolling ammeter or by any mechanical method of torque measurement.For control, the torque indications may be transmitted mechanically orelectrically to a dilution valve and so control the dilution rate as tomaintain a substantially constant consistency.

As will be seen from the graph in Fig. II the rate of increase ofviscosity becomes very high as the setting time is approached.Consequently, the actual viscosity maintained by the dilution may varyconsiderably without appreciably varying the time factor. Merely by wayof example, however, the viscosity may be held at substantially 20, 50or 100 poises. The dilution extends over a substantial period, e. g. 30minutes to 2 hours, depending upon the viscosity chosen and otherfactors. During this period the rate of addition of water is high atfirst and gradually diminishes as the rate of aging decreases. The stepcan be considered completed when the rate of Water addition becomesnegligible. During the dilution the pH increases only slightly; in atypical case the pH at the end of the dilution is 4.1. The amount ofwater used is preferably the minimum which will retain the chosenviscosity.

FURTHER AGING reduced time In the aging of the sol and the subsequentdilution step the silica miscellae are aged under strong acid conditionsat the maximum concentration while preventing the polycondensationreaction proceeding so far that a rigid hydrogel is formed. In the nextstep the material is given a short aging treatment under approximatelyneutral conditions while again preventing setting to a gel. This isaccomplished by bringing the pH to about '7, e. g. 6.0 to 7.0, whileadding a further quantity of water. The amount of alkali required isvery small, e. g. 0.06 volumes of 2.9 normal NH4OI-I. The amount ofwater required will again vary with the pH before the addition of thealkali, the concentration of silica and the viscosity chosen. In atypical case, for example, the amount of Water is about 4-5 volumes. Asin the previous dilution the rate of addition of the water is adjustedto maintain the viscosity (consistency) at an approximately constantvalue. At least a part of the Water is preferably added with the alkali,e. g. to produce a very dilute amor trona may be substituted forammonium hydroxide.

Only a very short time at a pH of about '7 is required and the timefactor at this point is not critical. Thus the re-acidification ofthesilica by the addition of aluminum sulfate may take place immediatelyafter bringing the pH to about 7, or any reasonable period of time mayelapse. In practice, the material may remain at a pH of '7 for about 5minutes to an hour, for example.

ADDITION OF THE ALUMINUM After bringing the silica to a pH of about 7 asdescribed, a solution of aluminum sulfate is added. This immediatelyreduces the pH to about 3 and materially reduces the viscosity. Thequantity of aluminum sulfate solution added is adjusted to give between18% and 30% of A1203 in the finished catalyst (dry basis).

In carrying out the preparation of the improved catalyst it is preferredto use an aluminum sulfate solution of high concentration. To this endit is desirable to use a substantially saturated solution, e. g. 1 molaraluminum sulfate. Aluminum chloride and aluminum nitrate are alsosuitable but are much more costly than aluminum sulfate.

HYDROLYSIS OF THE ALUMINUM SULFATE No appreciable reaction is believedto take place between the aluminum sulfate and the silica in the abovestep but other physical changes may take place. The reaction takes placeduring the hydrolysis step. The hydrolysis is carried out by therelatively slow addition of a basic precipitant such as ammoniumhydroxide. The final pH in this step is between about 5 and 7. Whenincorporating about 25% alumina this requires about 2.5 volumes of 2.9normal ammonium hydroxide. The addition of the ammonium hydroxide ispreferably begun shortly after adding the aluminum sulfate and ispreferably completed within about two hours of this time. The timefactor at this point is not exceedingly important. Other basicprecipitants such as trona, ammonium carbonate, ammonium hydrosulflde,may be employed if desired.

During the hydrolysis, which is preferably carried out by adding theammonium hydroxide at a relatively slow even rate (e. g. during 20minutes) with good mixing, an intermediate hydrolysis product reactswith the silica to produce a slurry of the desired silica-aluminacomplex. When the catalyst is prepared in the manner described thedesired large concentration of aluminum (e. g. 25% A1203) may beincorporated and combined with the silica in the desired manner. It isindeed possible in any of the older methods to physically incorporateany desired large concentration of aluminum, but at the expense of adecreased catalytic activity since free alumina, which acts as adiluent, is formed in the resulting catalysts. By the method of theinvention just described it is possible to incorporate larger quantitiesof aluminum in the particular complex form desired and the catalystcontains no free alumina.

REMOVAL OF ALKALI METAL IMPURITIES The wet catalyst at this stagecontains considto the method used, are present in a relatively highconcentration and their presence up to this stage is desirable. Aspreviously pointed out, these salts exert an .appreciable dehydratingeffect which tends to increase the effective concentrations of thealuminum sulfate. However, sodium salts are known to exert a detrimentaleffeet on the finished catalyst. There is some indication that smallamounts of sodium have less detrimental effect in the present catalystthan in previous catalysts.

There are several applicable methods for substantially completelyremoving sodium salts. In

. most cases it is sufficient to simply wash the undried material withwater which may be either condensate water or water freed of harmfulsalts by treatment with a base exchange resin. Alternatively, thematerial may be first washed to remove the bulk of the soluble salts andthen washed with a dilute acid, e. g. hydrochloric acid, hydrofluoricacid, acetic acid. Alternatively, the material may be given a finaltreatment with an acidic polyvalent metal salt solution, e. g. asolution of aluminum chloride, aluminum nitrate, or aluminum sulfate.Another. treatment which is very effective in removing sodium istreatments with a solution of an ammonium salt, e. g. ammonium chloride,ammonium nitrate, ammonium sulfate, ammonium acetate. While ammoniumacetate is very effective care must be exercised in its use since ittends to modify the pore structure. These treatments may be applied tothe filter cake obtained at this step of the process or they may beapplied after the filter cake has been partially dried. It is preferredto separate the catalyst from the mother liquor bysedimentation-decantation and to Wash out the sodium salts prior todrying.

DRYING After removing the sodium salts the material is dried. This stepis carried out in the conventional manner while observing the usualprecautions. It is preferred to pre-dry the material relatively rapidlybut yet under relatively mild conditions. One suitable method is to passthe -material in a thin layer through a drying oven held at betweenabout 80 C. and 130 C. while passing a stream of air to remove theevolved water vapor. Drying to a water content of about 15% isdesirable. This material may then be dried to a lower water content, c.g. 2-5%, by ordinary calcination at a higher temperature.

In an alternative method the material, before or after removing thesodium salts, may be made into a thin slurry which is passed through acolloid mill and then spray dried to form microspheres.

In another alternative method the material, preferably after removingthe sodium salts, may be made into a thick paste which is mulled untilit assumes a tacky consistency, then allowed to age and then finallyextruded into pellets which are dried in the conventional way.

TEMPERATURE CONTROL can be therefore; corrected either by heating or urefrigeration, or by slight adjustment of the other conditions in theknown manner.

The present method does not require either refrigeration or heating.However, both refrigeration and heating can be used to advantage iftheir use can be economically justified. Thus by cooling the sulfuricacid and/or the sodium silicate solution to below room temperature it ispossible to produce even more concentrated sols. Also, by heating thealuminum sulfate solution it is possible to use an evenxmoreconcentrated solution, e. g. 2 molar.

The reasons accounting for the improvements in catalytic propertiesefiected by the described method of preparation cannot be fullyexplained. As previously explained, one of the properties desired in thecatalyst is a low particle density. It is to be emphasized, however,that this property by itself is not responsive for the notedimprovement. It is well-known that the density of silicaal-uminacatalysts can be made low by any one of several methods. For instance,one method is to treat the material with hot water .for periods rangingfrom one to several days. Another method is to treat the material withdilute ammonium hydroxide. Simpleaging under alkaline conditions alsoproduces a material of lowerthan-usual density. However, these methods,although producing catalysts of low density. do not afford a catalysthaving the superior properties of the catalyst in question. In fact itis wellknown that in general the activity of silicaalumina catalystsdecrease with decreasing density. This is due not only to the lesserweight of catalyst occupying the reactor space but also to the fact thatin xerogel catalysts the available surface decreases markedly withdecreasing density. It will be noted that the catalysts prepared aspresently described have a high surface compared to what might beexpected from a low density material, but that the surface is slightlyless if anything than the conventional catalysts having densities of theorder 1.1 (usually considered optimum). If the specific activity(activity per unit of available surface) is considered,

however, it is found that the present catalyst, like that described inU. S. Patent No. 2,469,314, has a much higher intrinsic activity. It isevident therefore that when preparing the catalyst in the describedmanner the aluminum and silica are combined in such a manner as toafford a greater number of active sites per unit of surface. This resultis obtained by bringing the silica to just the proper state for reactionwith the hydrolyzing aluminum sulfate. This state is obtained by forminga very concentrated silica sol under acid conditions, allowing thesilica sol to partly polymerize under controlled acid conditions, thendiluting the sol at a point where T/T' approaches unity, and finallyraising the pH for a short period up to approximately '7. It will benoted that up through the point of adding the aluminum sulfate themaximum concentration of silica is maintained without at any pointallowing the material to set to a rigid gel. The use of lessconcentrated basic silica hydrogel slurries is, of course, commonpractice but such slurries even when alkaline give a more dense and lessactive high alumina catalyst. The preparation of the base gel under acidconditions likewise does not in itself afford the desired propertiesexcept when carried out as described in U. S. Patent No. 2,469,314 wherea very concentrated pH =O so] having an exceedingly long gel time isused. Thus, by way of example when silicate and sulfuric acid are usedthe material still has a density above 1.1.

EXAMPLES In the following examples the catalysts were tested through usefor the catalytic cracking of a. typical West Texas gas oil having thefollowing properties:

Gravity, A. P. I 30.7 A. S. T. M. boiling range, C 260-369 Aniline point70.2 Nd 1.4849 D4 (vac.) 0.8689 Bromine number 6 Carbon per cent weight85.65 Hydrogen d 12.86 Sulfur do 1.36 Nitrogen do 0.10

The cracking runs were made under a standardized fixed bed testprocedure using 50 cc. of the catalyst ([6-41 6-14 mesh granules) underthe following conditions:

Temperature, "C [565] 500 Liquid hourly space velocity 4 PressureAtmospheric Process period 1 hour Diluent None The catalysts were testedin the fresh condition and also after being subjected to artificialaging by treating them with steam for 24 hours at 565 C. and 1atmosphere pressure.

In the application of cracking catalysts it is the practice to contactthe hydrocarbon oil under cracking conditions with the catalyst in theform of finely divided particles, or in the form of granules, orpellets, or cast pieces. The catalyst particles quickly become fouledwith tarry materials and are usually regenerated first by steaming toremove easily volatilizable material and then by burning the lessvolatilizable residue. It has been observed that when used in suchprocesses the activity of the catalyst declines most rapidly during theearly period of use and thus generally levels out over an extendedperiod of use. The rapid initial loss of activity is largely caused bythe stripping steam. Relatively dry heating such as occurs in theforming process has very little damaging effect unless the temperaturesare allowed to greatly exceed the normal values of about 1050-1150 F.Therefore, in order to measure the stability of a catalyst it is commonpractice to subject the catalyst to an accelerated steaming treatmentwhich simulates the treatment to which ing a period of use. It has beenfound that a catalyst which declines only moderately under the mentionedsteaming treatment holds up well in commercial use and allows arelatively high equilibrium activity to be retained with a smallcatalyst replacement rate, whereas a catalyst which is badly damaged bysuch steam treatment affords a lower equilibrium activity at the samereplacement rate.

For the purpose of comparison the catalyst described in U. S. Patent No.2,469,314 may be used.

the catalyst is subjected durv .As pointed out in said patent thesuperior catalyst therein described and claimed, when tested under thesame conditions, was 116% as active on an equal weight basis as astandard catalyst. Also, as shown, upon steaming at 565 C. for 24 hoursthe catalyst declined to approximately 83 activity, whereas comparisoncatalysts declined on the same treatment to 48% and 45% activity on thesame basis.

Example I A catalyst was prepared as follows: Philadelphia QuartzCompany E-brand sodium silicate (4.17 N, 401 g. SiOz/L) was diluted to1.28 normal (as to Na+) and 3.2 volumes of the solution were slowlyadded to 1 volume of 4.1 normal sulfuric acid with stirring. Thisproduced a clear s01 having a pH of about 3.5 and containing about 93grams SiOz per liter. After allowing the sol to ,age for approximately61 minutes (T/T' approximately 0.8) a total of 2.25 volumes of waterwere added with stirring over a period of about '77 minutes at a rate tomaintain the viscosity substantially constant. This resulted inincreasing the pH to about 4.1. The pH was then increased to 7.0 by theslow addition (about 10 minutes) of about 0.06 volumes of 2.9 normalammonium hydroxide while the viscosity was again held substantiallyconstant by the addition of approximately 4 volumes of water. After aperiod of about 12 minutes, sufficient 1 molar aluminum sulfate solutionwas added to supply about 22% A1203 on "the dry basis. This resulted indecreasing the pH to about 3.0 and in reducing the viscosity sharply.Then the aluminum sulfate was hydrolyzed by slowly adding 2.9 normalammonium [hydroixde] hydroxide until the pH was about 7 (about 2.5volumes). The material was then filtered and the wet catalyst was washedwith water until the wash water was free of sulfate. The washedalumina-silica complex was dried at C. and then calcined for 6 hours at565 C. in a stream of dry air. The physical properties of the catalystare compared with those of the catalyst of Example 11 of U. S. PatentNo. 2,469,314 in the following table:

Example Compari- I son Both catalysts were tested fresh and aftersteaming for 24 hours at 565 C. The results are shown in the followingtable:

- Example I Comparison Fresh Steamed Fresh Steamed Per cent cracked 49.3 42.4 43.8 as. 5 Per cent converted to 50ZO0 0. fractions. 22. 4 20. 519. 7 19. (l

1 In all cases per cent cracked means minus the per cent by Weight ofrecovered oil of the same boiling range as the feed. I

I In all cases activity means the activity per unit weight of catalystcompared to the same standard as used in U. S. Patent No. 2,469.314(catalyst A).

It will be noted that the physical properties of the two catalysts aresubstantially the same except that the catalyst of Example 1 containsThe sodium e'e,4ae

sodium than would be desired. content can, however, easily be rewashingor by one of the methods described above. It will be noted that thecatalyst prepared by the new method is more active both initially andafter being subjected to the. relatively drastic steaming treatment.This is an important advantage. However, of even more importance is thefact that the catalyst. can be produced much more cheaply by the newmethod. Little acid is uselessly consumed; no long aging or treatingperiod requiring large acid resistant agitators are involved; a rigidhydrogel is avoided; the catalyst can be washed either by sedimentationand decantation, or by filtering with washing on the filters, or byrepulping; refrigeration or heating, while they can be advantageouslyused, are unnecessary.

Example II A catalyst was prepared essentially as described in Example Iexcept that the material after dry ing at 90 C. was treated with anaqueous solution of ammonium acetate to decrease the content of N320toless than 0.01%. The particle density of the catalyst was 0.94 g./cc.The results obtained on testing this catalyst before and after steamingare shown in the following table; MM

Example II Comparison a Fresh Steamed Fresh somewhat more Steamed Percent by weight cracked 50. 5 -12; 2 43. 8 38. 5 Per cent by weight 50-200 0. fraction 22. 5 20.4 19.7 19. 0 Activity 135 83 116 83 R It willbe noted that, contrary to what would be expected on the basis of priorexperience With silica-alumina cracking catalyst, the 0.17% NazO in theincompletely washed catalyst of Example I had very little, if any,detrimental efiect.

Example III A catalyst was prepared essentially as described in ExampleI, except that the pH of the sol was adjusted to 3.91 instead of 3.5.The resulting sol therefore aged more rapidly under slightly less acidconditions. The dilution with water was therefore begun about 24 minutesafter forming the sol (T/T'=about 0.8).

The physical properties and the results of testing the catalyst aregiven in the following table:

Example III Comparison 'Fresh Steamed Fresh 7 Steamed Average porediameter, 6 A 5e 5e a Per cent by w ght cracked 48.6 40.6 43.8 38.5 Percent by weight 50 200 0. fraction 22. 4 I 19. 7 19. 7 -19. 0 Activity130 I 83 116 83 Example IV A catalyst was prepared essentially asdescribed in Example I, except that in hydrolyzing the aluminum sulfatethe final pH was brought to 6.4 instead of 7. The properties andresultsof'testlng the'c talyst are given in the following A catalyst wasprepared as follows: Philadelphia; Quartz Company E-Brand sodiumsilicate was diluted to 2.06 normal and 1.95 volumes of the solutionwere added simultaneously with 1 volume of 4.07 normal sulfuric acid to1.2 volumes of' water while stirring. The solutions were added at such arate that the pH during the formation of the sol was substantiallyconstant at 2.5. Upon completion of the addition of the sodium silicateand sulfuric acid the pH of the resultant sol was adjusted to 3.5 by theaddition of a small amount of sodium silicate solution. The resultingsol contained about 93 grams of S102 per liter. After aging for about 46minutes (T/T" approximately 0.8) the addition of water was begun and theremaining part of the preparation was carried out essentially asdescribed in Example I. The properties and results of testing thecatalyst are given in the following table:

Example V Comparison Fresh Steamed Fresh Steamed Analysis:

N340 A1203. S O 4 Average pore diameter,

Per cent by weight cracked Per cent by weight 50- A 0. fraction ActivityWhile the catalyst prepared by the method described is a particularlyactive and stable cracking catalyst and is designed to allow the maximumefiiciency in catalytic cracking, it can be applied, if desired, inother processes where one or more of the reactions involved in catalyticcracking is important. For example, the cata-- lysts prepared in thedescribed manner are more acidic in nature than silica-alumina catalystsprepared in the usual manner and they therefore are more active for acidcatalyzed reactions, e. g. isomerization, polymerization, alkylation,hydrogen transfer. The catalyst loses its high activity for suchreactions more rapidly than it does its activity for C--C bond fission.The catalyst may therefore be advantageously used for catalyzing one ormore of such reactions, e. g. isoforming, for a period of time and thenbe used for catalytic cracking with little loss of efiiciency in thecracking process. Also the catalyst, after being substantially spent incatalytic cracking,

,may still be used advantageously for processes 13 where only a verymild cracking is desired in connection with an acid nature, e. g. in thepreparation of cracking feed stocks from heavy residues by catalyticviscosity breaking.

The invention claimed is:

1. In the preparation of a silica-alumina cracking catalyst theimprovement which comprises (1) preparing a silica sol containing atleast 85 grams S102 per liter by mixing a sodium silicate solution witha sulfuric acid solution 9 under acid conditions with a final pH between2.8 and 4.1, (2) aging said sol at a pH in said range for a time whichis at least 0.5 but less than 1 times the time of set of said S01, (3)at said time diluting the sol with water at a rate to maintain theviscosity substantially constant, (4) then increasing the pH up to aboutpH '7 by the addition of an alkali while adding water at a rate tomaintain the viscosity substantially constant, (5) adding a concentratedsolution of aluminum sulfate in an amount sufficient to provide between18% and 30% A1203 on the dry basis, (6) hydrolyzing the aluminum sulfateby the addition of a basic precipitant until the pH is between 5 and '7,and ('7) washing and drying the product.

2. In the preparation of a silica-alumina cracking catalyst theimprovement which comprises (1) preparing a silica sol containing atleast 90 grams S102 per liter and having a pH between 2.8 and 4.1 bymixing a sodium silicate solution with a sulfuric acid solution underacid conditions, (2) aging said sol at a pH in said range for a timewhich is at least 0.5 but less than 1 times the time of set of said sol,(3) at said time diluting the sol with water at a rate to maintain theviscosity substantially constant, (4) then increasing the pH up to aboutpH '7 by the addition of an alkali while adding water at a rate tomaintain the viscosity substantially constant, (5) adding a concentratedsolution of aluminum sulfate in an amount sufficient to provide between18% and 30% A1203 on the dry basis, (6) hydrolyzing the aluminum sulfateby the addition of a basic precipitant until the pH is between 5 and '7,and ('7) washing and drying the product.

3. In the preparation of a silica-alumina cracking catalyst theimprovement which comprises (1) preparing a silica sol containing atleast 90 grams S102 per liter by mixing a sodium silicate solution witha sulfuric acid solution under acid conditions and adjusting the pH ofthe sol to about 3.5, (2) aging said sol at said pH for a time which isat least 0.5 but less than 1 times the time of set of said sol, (3) atsaid time diluting the sol with water at a rate to maintain theviscosity substantially constant, (4) then increasing the pH up to aboutpH '7 by the addition of an alkali while adding water at a rate tomaintain the viscosity substantially constant, (5) adding a concentratedsolution of aluminum sulfate in an amount sufficient to pro- 14 videbetween 18% and 30% A1203 on the dry basis, (6) hydrolyzing the aluminumsulfate by the addition of a basic precipitant until the pH. is between5 and '7, and ('7) washing and drying the product.

4. In the preparation of a silica-alumina cracking catalyst theimprovement which comprises (1) preparing a silica sol containing atleast grams SiOz per liter and having a final pI-I between 2.8 and 4.1by adding a sodium silicate solution with stirring to a sulfuric acidsolution, (2) aging said sol at said pH for a time which is at least 0.5but less than 1 times the time of set of said sol, (3) at said timediluting the sol with water at a rate to maintain the viscositysubstantially constant, (4) then increasing the pH up to about pH '7 bythe addition of an alkali while adding water at a rate to maintain theviscosity substantially constant, (5) adding a concentrated solution ofaluminum sulfate in an amount suflicient to provide between 18% and 30%A1203 on the dry basis, (6) hydrolyzing the aluminum sulfate by theaddition of a basic precipitant until the pH is between 5 and '7, and('7) washing and drying the product.

5. In the preparation of a silica-alumina cracking catalyst theimprovement which comprises (l) preparing a silica sol containing atleast 85 grams S102 per liter by simultaneously adding with mixing asodium silicate solution and a sulfuric acid solution into an acidaqueous medium and then adjusting the pH of the mixture to about 3.5 bythe addition of a small amount of an alkali, (2) aging said sol at saidpH for a time which is at least 0.5 but less than 1 times the time ofset of said sol, (3) at said time diluting the sol with water at a rateto maintain the viscosity substantially constant, (4) then increasingthe pH up to about pH '7 by the addition of an alkali while adding waterat a rate to maintain the viscosity substantially constant, (5) adding aconcentrated solution of aluminum sulfate in an amount sufficient toprovide between 18% and 30% A1203 on the dry basis, (6) hydrolyzing thealuminum sulfate by the addition of a basic precipitant until the pH isbetween 5 and '7, and ('7) washing and drying the product.

6. Process according to claim 1 in which the aluminum sulfate solutionis at least 1 molar and is added in an amount sufficient to provideabout 25% A1203 on the dry basis substantially immediately afterincreasing the pH up to about pH '7 in step 4.

'7. Process according to claim 1 in which the dilution of the sol withwater in step 3 is begun at a time T where the ratio of T/T approaches0.95, where T is the time of set of the sol.

LLOYD B. RYLAND.

No reference cited.

